# MCQs on Power Systems

01․ Length of the cable is doubled, its capacitance C will be

The length of the cable and the capacitance of the cable are directly proportional to each other. Hence, if the length gets doubled, then the capacitance also can be doubled.

02․ Tarapur nuclear power plant has which type of reactor?

The Tarapur Atomic Power Station (T.A.P.S.) is located in Tarapur, Maharashtra, India has initially built with two boiling water reactor with the capacity of 210 MW on 1969. But, now this plant has two extra pressurized heavy water reactor with the capacity of 540 MW on 2006.

03․ Which of the following rotor is used in thermal power plants?

Cylindrical rotor is also called as round rotor or smooth rotor, there is no projection, there a closed portion contain field winding which is distributed and unslotted portion also acts as poles . It has large axial length and small diameter, resulting high peripheral speed. As the air gap is uniform throughout the machine it is more suitable for high speed operation, employed in all thermal, nuclear power plants containing turbo alternators with two or maximum 4 poles only.

04․ Four identical alternators each are rated for 20 MVA, 11 KV having a subtransient reactance of 16% are working in parallel. The short circuit level at the busbar is

05․ India’s largest thermal power station is located at

The plant was officially inaugurated by the then Prime Minister Indira Gandhi on 8th October, 1984. With the total capacity of 3340 MW and this plant is largest thermal power plant in the India. It accounts to more than 25% of total Maharashtra needs.

06․ Oxide film arrestor has which of the following properties?

The both properties are essential properties of an oxide film lightning arrestor.

07․ What is the total installed power capacity (MW) in West Bengal as published by ministry of power in 2011?

This table describes the total installed power capacity in the eastern region. Hence, in WB alone approximately 8200 MW of power capacity is installed.

08․ What should be the minimum depth (in metre)of cable trench to dug for laying of 1.1 kV?

The below diagram show the length and depth for different level of voltages and different number of cables. Hence, for a 1.1 KV line, the depth range is 750 mm or 0.75 meter. And side space between the wall and cable is 25 mm or 0.025 meter..

09․ NTPC (National Thermal Power Cooperation) has its only thermal power generating unit in West Bengal at

Farakka super thermal power plant is under the thermal power generating unit of NTPC in West Bengal. The actual place is P.O. Nabarun - 742 236, Dist. Murshidabad, West Bengal.

10․ If the fault current is 2000 A, the relay setting is 50% and CT ratio is 400 : 5, then plug setting multiplier will be

The current transformer ratio is 400 / 5. So, the CT can be provided a rated current of 5 Amps to the relay coil. Thereby the rated relay current is 5 Amps. If the relay setting is 50%, then the relay can be operated for 5 × ( 50 / 100 ) = 2.5 Amps. This is the pick-up current of that relay. We know that the fault current is 2000 Amps. Hence, the fault current in the secondary of the CT is 5 × ( 2000 / 400) = 25 Amps. Hence, the plug setting multiplier = 25 / 2.5 = 10. That means the fault current in the secondary of the CT is ten times greater than the operating current of relay coil.

11․ Galvanised steel is generally used as

If the wires are made up with some other ordinary steels, rust and corrosion attacked the wire after some time due to the environmental wet conditions. A layer of zinc oxide can be provided on the steel wire by some chemical process. This zinc oxide layer protects the steel wire from the rust and corrosion effects. That’s why galvanized steel is used in many places.

12․ Plug setting of a relay can be altered by varying

The minimum pick up value of the deflecting force of an electrical relay is constant. Again the deflecting force of the coil is proportional to its number of turns and electric current flowing through the coil. Now, if we change the number of active turns of any coil, the required electric current to reach at minimum pick value of the deflecting force, in the coil also changes. That means if active turns of the relay coil is reduced, then proportionately more electric current is required to produce desired relay actuating force.

13․ Objectives of power system is/are

Objectives of power system are
1. Cost of electrical energy per KWh is to be minimum
2. Rated voltage and frequency has to be supplied to the consumers
3. Reliable power has to be available
4. Effective protection system has to be used for isolating the faulty section and keeping other sections healthy.
5. More stable generators are to be used, so that it should not lose synchronism under faulty condition.
6. Flexible power has to be available.

14․ Objectives of power system is/are

Objectives of power system are
1. Cost of electrical energy per KWh is to be minimum
2. Rated voltage and frequency has to be supplied to the consumers
3. Reliable power has to be available
4. Effective protection system has to be used for isolating the faulty section and keeping other sections healthy.
5. More stable generators are to be used, so that it should not lose synchronism under faulty condition.
6. Flexible power has to be available.

15․ The main objectives of electrical power transmission is/are

Objectives of electrical power transmission are
1.Transmission system must be more efficient with minimum line losses and maximum power transfer capability
2. Voltage regulation of the transmission line must be zero or minimum

16․ Advantages of higher transmission voltage is/are

Advantages of higher transmission voltage are
1. Power transfer capability of the transmission line is increased
P

_{max}= V_{s}*V_{r}/X_{s}Where, V_{s}= Supply voltage V_{r}= Receiving end voltage If V_{s}= V_{r}, Pmax ∝ V_{s}² 2. Transmission line losses are reduced Power P = VI cosφ I = P/(V cosφ) Transmission line losses P_{l}= I²R Therefore, Transmission line losses P_{l}∝ 1/V² 3. Area of cross section and volume of the conductor is reduced Resistance R = ρl/A Where, ρ= resistivity l = length of the conductor A = Area of cross section Therefore area A ∝ 1/V²17․ Which of the following statement is true

At higher voltage, volume of conductor is reduced.
Area of conductor A ∝ 1/Vs²
Where Vs = Supply voltage
So that material requirement is reduced and hence cost of the material and transmission is reduced.

18․ Maximum power transfer capability of transmission line can be increased by

Maximum power Pmax ∝ V

_{s}²/X_{s}Maximum power transfer capability of transmission line can be increased by either increasing voltage level or reducing the line reactance value. Methods of reducing line reactance are 1. Parallel transmission lines 2. Using series capacitance 3. Using bundled conductors19․ For flat voltage profile system, voltage regulation is

% Voltage regulation = (V

_{s}-V_{r})/V_{r}*100 Where, V_{s}= Supply voltage V_{r}= Receiving end voltage For flat voltage profile system V_{s}= V_{r}Therefore, voltage regulation for flat voltage profile system is 0%.20․ Maximum power transfer in a transmission line can be obtained by

Maximum power Pmax ∝ V

123>>>
_{s}²/X Where V_{s}= supply voltage X = reactance Maximum power transfer capability of transmission line can be increased by either increasing voltage level or reducing the line reactance value. Methods of reducing line reactance are 1. Parallel transmission lines 2. Using series capacitance 3. Using bundled conductors